I recently bought a 1988 Limited that has a cold, extremely long crank issue. I found this thread searching which is long but never got down to the answer to the problem. I am having the exact same issues as this thread and decided to start a new thread as that one is pretty old. https://www.cherokeeforum.com/f2/hel...-start-212974/

This Cherokee does have some wiring issues as a mouse/rat took up residence under the hood, built a nest and proceeded to munch on the wiring harness. The harness has many patches already in MANY places but all are soldered and solid. If anybody has a 88 engine bay harness, I would love to buy it!! I do have one mystery wire that was bundles up and I dont know if it should go to something but have checked every plug and nothing is missing, or just an extra wire in the harness, it is Orange and about 4' long with a terminal on the end, check pics below.

It takes 3 long cranks before it starts firing and then stumbles a bit and then idles perfectly and runs good after that. If you shut it off and restart, it starts a little easier but not like it should. Once its warmed up and driven a bit, it starts fine. After searching many threads, I first checked fuel pressure and got 40psi with just the key on and a solid 31psi when running and after letting it set with the engine and key off, 4 hours later its still at 30psi so that checks out OK. I have tried cycling the key several times as if I did have a pressure issue and still starts hard. Then I started doing Cruiser54's mods/checks and have performed the following...1,2,3,4,5,6,7,8,9,11,21, 22 and 31 all with no changes. I did end up eliminating the C101 plug. I checked the CPS and got 4.9vac but bought a new Napa one and drilled the upper hole to 3/8 and installed and still get 4.9vac when cranking. I also changed the oil/filter, new fuel filter, new plugs gaped at .035, new rotor, cap and wires, again, no change. Per the other thread, when I do the first long crank, I can smell gas at the TB and exhaust and I have tried on a cold start using one 1 second shot of starting fluid in the TB and it fires right up not problem. I have not cold cranked it and then pulled to plugs to see if they are wet but that is next on the list but I have checked for spark when cranking at every wire and its good and bright. I have made up all new 4ga ground wires and 2ga positive cables and added a ground from the battery to the body next to the battery. I have tried bypassing the ballast resistor with no difference. I do have rebuild injectors coming to put in as it probably needs it anyway.

Any new thoughts from the experts? Like I said, if anybody reading this has a whole engine bay harness, I would love to get it.

Thanks


Mystery wire I found bundled up

Terminal on the end of the mystery wire

 

Wow. Very thorough. I'm impressed.
Have you ever tried the "poor man's prime"?
Turn the key to ON and let the fuel pump prime. Turn the key OFF. Wait a few seconds and start the Jeep.

 

Do you know where the other end of that orange wire goes? I'm not sure the terminal is the right size but orange runs around to the other side to connect a few things like the EGR solenoid and fuel pump ballast resistor.

Here's the crank sequence that may help troubleshoot.

"CRANK MODE OPEN LOOP
During engine cranking, the ECU receives Information from the following Inputs:

Coolant temperature sensor
Manifold air temperature sensor
Manifold absolute pressure (MAP) sensor
Throttle position sensor
Starter relay
Engine speed sensor signal
Sync signal generator
Battery voltage

The engine crank Input from the starter relay provides a signal to the ECU to energize the fuel pump relay and to begin the start sequence. The ECU determines the correct cranking speed (approximately 300 rpm) by counting the flywheel teeth passing the speed sensor. With the proper cranking Input the ECU will synchronize the fuel injector opening and the spark plug firing. The ECU determines the correct Injector pulse width and opens the injectors in the proper order by supplying a battery voltage signal;

The sync signal input from the distributor provides the signal needed by the ECU to locate number one or number six piston. When the number one or number six piston Is on its exhaust stroke, and the ECU receives all other crank mode Inputs, the ECU energizes the injector for that piston. The ECU uses either piston one or piston six as the number one in the tiring order. If the ECU does not receive a sync signal input, it will randomly select an Injector as number one in the tiring order and use it to sequence the fuel injectors. The engine will probably start, but performance wit be noticeably poor."

My '88 (208K) takes about 4-5 seconds of cranking on a cold start (well cold for SoCal). About half that when already warm.

Pic of fender well:



Cruiser has some technical documents on his site too, besides tips.

 

Yes one of the first things I tried, have tried primer 3 key turns to 10 key turns and it makes no difference. I have gone over and over your site Cruiser, great and helpful info, I scanned through the Renix Manual last night. Looking through wiring diagrams, orange feeds a lot of things in the harness and need to figure that out. It comes out of the loom on the passenger side about half way down the fender and just need to see where all it would reach.

 

OK, this has overnight turned into a total no start situation. Check fuel pressure again and still good, checked spark and have good strong blue spark, pulled a plug after cranking and plug is dry, motor fires and dies on starting fluid. Borrowed a noid tester and nothing at the injector plugs on all 6 cylinders. Checked the CPS and got .36vac when cranking on a brand new Napa sensor so I swapped out to the original one that was in the motor when I got it which was a Standard CPS and still got around .35-.38vac. I picked up a new CPS, Standard brand, put it in and try starting the motor and it intermittently 3-4 times on the first crank but nothing on every crank after that. I check the CPS again and get .35-.38vac on the brand new sensor, checked with 3 different multimeters. Still no fire at the injector plugs with the noid tester. Originally the grounds that are suppose to go to the dipstick stud were on the valve cover and it was at least starting at that time then I cleaned and moved them to the dipstick stud but it did at least start with a long crank, moved it back to ta valve cover stud and still have a no start, moved back down to dipstick stud after a good cleaning of everything and still no start. Battery is fully charged and cranking over good. Getting to my whits end here, so what else can cause the injectors to not fire? It does have a remanufactured computer and I guess that could be it but dont have another to try as my son and friends all have a newer Cherokee and our local wrecking yard just went out of business and scrapped everything. Like I said, it was long crank starting the night before and the next day nothing.

 

Nice blue spark?

 

Bright spark, not necessarily Blue. I have been cranking and testing for a while now and while the plugs are black, they are not wet at all. One little thing I just noticed while cranking is the temp gauge pegs to the right when cranking, is this normal? This Cherokee did have the CPS recall/TSB done on it where the sensor plug wires were cut from the harness and run directly to the plug on the ECU and I tested the vac while cranking at the computer plug and got .36vac there, the same as I get from the sensor plug so the signal is getting to the ECU.

 

Not familiar with the '88 specifics but I'd think it would not be normal for that year either to have it pegged to the right when cranking..

 

There are 6 injector drivers in the ECU. Doubtful they all failed.
Makes no sense that the injectors won't fire when you have spark. CPS is obviously working.
Have you checked the ground wires at the injectors to the negative battery post for resistance?

 

Ok here is where we are at now. I had 3 CPS sensors that 2 were new but they all were showing around .35vac. My son helped me and he found a post about possibly shimming the CPS with washers so we tried it and we saw .41vac so we started tweaking it a bit but it dropped to .14vac. I took it and removed the washers and then using a vice and adjustable wrench gently twisted the mounting plate so that tip of the sensor angled toward the block, probably 2-3 degrees and the first test we got .60vac and after making sure the bolts were tight, it’s consistently .55vac so that looks good. I also tested the CPS at the ECU plug pins and get the same reading. I then checked the injector ground resistance you suggested and 1-6 all measured .001 ohms. Tested the fuel pressure again and it’s still good….Any other ideas?

 

Review Post 9.

 

Yes I mentioned in my last post I checked them and all read .001 ohms resistance.

 

Sorry.

 

OK so this morning I tested for continuity from the computer plugs to the other end of the harness in the engine bay. Checked C11/D10 to all the end points based on the wiring diagram and all were good. Tested B1,A3,A1,A4,B2 and A2 from the plug to the injector plugs and all good. Proceeded to test every other pin on the plug to the sensor plugs including grounds and all check out good so it looks like everything can talk to the computer.......could the ECU be toast? May open it and take a look. Could the NSS cause this? After I got all done, I plugged everything back in and again absolutely no attempt to even fire while cranking, had good spark and after cranking, checked a couple plugs and they were dry, fuel pressure was good and would still fire when I gave it a shot of starting fluid. Tried bypassing the Ballast resistor again with no luck, new fuel pump relay no luck. I also checked for continuity through the fuable links thinking one may be broken but they all checked out good.

 

worth a try.